Model-based approach to improve class 1 AVO attributes

Abstract

We propose a model-based Amplitude Variation with Offset (AVO) approach to address the assumption of weak elastic contrast in the linearized approximations of Aki-Richard equation. Existing approximations, especially for the Class 1 AVO response, which indicates the positive elastic contrast, deviate significantly from the Zoeppritz equation in presence of large elastic contrast. Results of the proposed approach show that it can minimize the deviation from the Zoeppritz equation, improve AVO attributes, and is capable of providing the desired attribute for characterizing a reservoir. The method starts with two matrices. One matrix is of the simulated rock properties termed as the rock-property-matrix and the other of the Zoeppritz AVO responses for those rock properties termed as the response-matrix. A model-based AVO equation or the basis-function-matrix is computed utilizing the rock-property-matrix and the response-matrix. The inverse of the basis-function-matrix is applied to the real data to get the AVO attributes from this approach. The conventional AVO (Aki-Richards) and model-based AVO attributes are compared in a class 1 AVO environment from the offshore east coast of India. The curvature attribute based on model-based AVO shows significant improvement. The synthetic-seismic correlation of the curvature attribute improves from −0.03 to 0.9 while synthetic-seismic correlation of the gradient attribute improves from 0.5 to 0.77. The improved AVO attribute volumes add significant values in the reservoir characterization.